The present invention relates to apparatus for retaining nozzles stacked one against the other in a groove of a carrier of a turbine. The invention particularly relates to a new nozzle retention key for retaining the nozzles in carrier grooves at the horizontal joint faces between upper and lower carrier halves, which does not require mechanical fastening of the key to the carrier.
In steam turbines, there is typically an annular carrier for supporting the axially spaced, circumferential arrays of fixed nozzles. The annular carrier is usually divided into a pair of carrier segments or halves, each of which extends arcuately 180°. The carrier halves are secured to one another at opposed horizontal joint faces to form a 360° array of nozzles at each axially spaced turbine stage position. Typically, the nozzles comprise an airfoil having a radial outer dovetail-shaped base for reception in a generally correspondingly dovetail-shaped groove in the carrier. Generally, the opposite side faces of each base of the respective nozzles are angled relative to the axis of the turbine, enabling the base to accommodate the angularity of the airfoil. When the nozzles are installed in each carrier half groove, the nozzle bases are stacked one against the other within the grooves forming a semi-circular array of nozzles.
The first nozzles loaded into a carrier, especially the carrier upper half, require a retention key to prevent the first and subsequently added nozzles from falling out of the dovetail during assembly. This same problem can also surface in connection with both the upper and lower carrier halves during disassembly or shipping of the carrier segments.
One current key design requires a machined pocket in the carrier at the horizontal joint face; a tapped hole in the machined pocket; and a screw to retain the key in the pocket.
There is a need for a new key design that eliminates the screw and the need for tapping the carrier to thereby also eliminate the possibility of breaking either a tap or a screw in the carrier.